A loudspeaker is a transducer which converts an electrical signal into sound. Audio data is amplified to drive an actuator which moves a diaphragm member back and forth to produce sound waves. In a typical dynamic loudspeaker the actuator is a voice coil and the diaphragm element is a cone or membrane.
If a loudspeaker is excited at power levels which are too high, the excursion of the diaphragm member can be greater than it is designed for and it can become damaged. Loudspeakers can also be damaged by overheating of the actuator, diaphragm member or other elements.
These problems are especially acute in the example of loudspeakers of mobile devices, such as cell phones, tablet computers, laptops and the like. Mobile devices may come into contact with a number of different surfaces formed of different materials, and are generally subject to harsh and unpredictable stresses as they are stored in pockets or bags, and used in a variety of indoor and outdoor environments.
Furthermore, there are strict design constraints that effect loudspeaker designs for mobile devices. The loudspeakers have to be small in area, but also to be very thin and to provide a high sound level. These are difficult criteria to reconcile, and so the loudspeakers of a mobile device tend to operate close to their performance limits and are prone to damage by overexcursion or overheating.
The frequency response of a loudspeaker is also subject to manufacturing tolerance and drift due to aging, external shocks and environmental conditions such as dust and humidity.
A changing or unpredictable frequency response poses several problems. The accurate reproduction of sound may be compromised because equalization of the sound across frequency bands does not operate as expected. Also, a loudspeaker may be more prone to damage by overexcursion or overheating if the frequency response is altered.